Object I was sculpting disappeared in Sculpt mode, how do I get it back?
You're in Local View. This hides all other objects. It can happen that you selected another object or deleted the local object, and now the view shows nothing or always the wrong object. This happened a few times to me and I wondered where my stuff was gone.
To exit this view press Numpad+/ or use the menu: View → Local View → Toggle Local View
Hope that helps...